When it's a hentai I'm ok ish with it because it's admitedly something for degenerates. When it's a casual manga it's supposed to be a "normal" read. It's "normalising" pedophilia.
... you sent a letter? Bro, make sure you get a response before you dump your child on someone. Friend or no, if we're not actually discussing this and it just happens, I'm reporting your ass to CPS.